The present invention relates to an internal combustion engine induction air volume calculating apparatus.
It is a conventional practice to detect the volume of induction air that passes a throttle valve with an air flow meter so as to determine a fuel injection volume according to the detected induction air volume.
However, when a secondary air is supplied to the air induction pipe at a portion downstream (an internal combustion engine side) of the air flow meter by, for example, a brake booster (a vacuum servo unit), a larger volume of air than the induction air volume detected by the air flow meter or the volume of induction air that passes the throttle valve is supplied to the internal combustion engine. Due to this, air-fuel mixture becomes lean and, in particular, when the engine is idling, there is caused a drawback that the idle speed of the internal combustion engine is lowered.
To cope with this, for example, there is proposed an idea of providing a brake switch for outputting a signal corresponding to the operation of the brake booster, so that a correction control is carried out to prevent a decrease in engine rotational speed when it is detected that the brake is released or the secondary air is supplied from the brake booster (refer to, for example, Patent Literature No. 1).
[Patent Literature No. 1]
The Examined Japanese Patent Application Publication No. Hei3-48340 (from page 3 to page 4)
In the related art, however, while whether or not the secondary air is supplied from the brake booster can be detected, an increase in induction air that is supplied to the internal combustion engine cannot be detected. Therefore, the correction control has been unable to be implemented with good accuracy. In addition, there has been a drawback that, in the event that the brake switch fails, the implementation of the correction control becomes impossible.
Note that the drawbacks are associated not only with the secondary air supplied from the brake booster but also with secondary air supplied from, for example, an EGR unit (an exhaust gas recirculation unit), a purge mechanism, or a PCV unit (a blow-by gas recirculation unit) to the air induction pipe at a position downstream of the air flow meter.